We will investigate the mechanism of energy transduction and its regulation in the actin-myosin system by determining the positions of certain functionally important sites in the myosin molecule and the actin-S1 complex. We will prepare specimens of myosin and of acto S1 in which known sites have been labeled with a heavy metal cluster compound and will examine these specimens by high-resolution scanning transmission electron microscopy and by low-dose conventional transmission electron microscopy in order to visualize the labeled positions. By computational analysis of the data and comparison with existing models for the myosin molecule and the acto S1 complex, we will determine the positions of the labeled sites relative to each other, to the actin-S1 contact and to the S1/S2 junction.